Scientists have discovered new antibodies that neutralize viruses that cause dengue, potentially putting a universal vaccine within reach for a mosquito-borne illness that strikes an estimated 400 million people a year.

The antibodies are effective against all four dengue viruses, according to an article published today in Nature Immunology. A vaccine being developed by Sanofi (SAN) has had mixed results, helping to protect people from three of the viruses in one trial, and in all four in a bigger study.

Dengue is carried by mosquitoes and is common in the tropics, with Brazil and Indonesia reporting the most cases. About a quarter of those infected develop symptoms, with most enduring pain and a fever that lasts about a week. The most severe cases develop hemorrhagic fever, which can be fatal. About 20,000 people die from dengue each year, according to the World Health Organization.

Dengue has spread “exponentially” over the last 50 years, leading to epidemics that have virtually shut down cities, said Gavin Screaton, a professor at Imperial College London and the lead author of the paper, told reporters. “Without a vaccine, it’s unlikely that this disease will ever be controlled.”

Imperial College has filed for a patent to protect its discovery, Screaton said in an interview. The university may eventually license or sell its intellectual property. Besides Sanofi, other companies working on dengue vaccines include Osaka, Japan-based Takeda Pharmaceutical Co. (4502) and Merck & Co. (MRK)

Sanofi effort

Sanofi, the Paris-based company that has developed polio vaccines, is investing an estimated $800 million in clinical trials and a manufacturing plant to come up with dengue drugs.

A worker at Sanofi's dengue vaccine plant in Neuville-sur-Saone, France. Sanofi, the Paris-based company that has developed polio vaccines, is investing an estimated $800 million in clinical trials and a manufacturing plant to come up with dengue drugs.

The researchers analyzed monoclonal antibodies -- proteins produced by the immune system -- from human patients who were infected with the virus. In lab tests, the “extremely potent” antibodies were capable of neutralizing dengue in insect and human cells, Screaton said.

Dengue victims become immune to the virus that infects them, but become more susceptible to other versions of the virus.

“If you’re going to get very, very sick, it’s far more likely when you’re infected for the second time,” Screaton said. “There’s something about the immune response form the first bite that primes you for a second infection.”

Researchers theorize that dengue has become more virulent because the four viruses, once isolated in remote tropical regions, are now mixing as globalization means people and goods bring them together. The disease takes hold in cities because mosquitoes thrive where they find stagnant water, such as tire dumps and construction sites.